I believe it will be useful. Nikon is making a step in the right direction. Seriously if my pns can do both photography and videography, why can't a more expensive dslr do likewise?
Besides, there's an advantage of using different lenses for different effects, or get excellent sharpness in your video.
Perhaps the technology is still new, AF is not available etc. Give it some more time to mature.
True, there is always a right for the right job. Back then, a fax machine, a printer, a scanner and a copier were separate machines. Now with advancement in technology, I can have all of them in 1 at a price of $400? And it works fantastically. So will you be rejecting the all-in-one machine? If technology today has the means of combining multiple functions into 1 tool, I think it should be embraced rather than rejected.